(1) Field of the Invention
The present invention relates to a touch panel, and more particularly, relates to a supporting structure of the touch panel.
(2) Description of the Prior Art
With the development of science and technology, there is a tendency toward diversification among the input devices of electronic product. Besides the typical input devices such as keyboard or mouse, a touch panel, one of the input devices, becomes much more popular than before. A touch panel with fingerprint identification function can be applied to a user identification system of electronic products, such as notebook computer, PDA and cell phone, or be applied to a door control system, especially for some research institution, hi-tech company, or military unit. In last years, the touch panel is integrated with the display (or monitor) of a tablet computer. Therefore, an user can operate the tablet computer by touching or writing on its monitor.
Referring to FIG. 1 is show a typical resistive touch panel 10. This kind of touch panel 10, which is applied to an electronic apparatus as its input device, has no fingerprint identification function. The touch panel 10 comprises a conductive sheet 12, an elastic conductive film 16, a plurality of ball spacers 14. The plurality of ball spacers 14 are formed between the conductive sheet 12 and the elastic conductive film 16 formed above the conductive sheet 12, to make the conductive sheet 12 separate from the elastic conductive film 16.
Two opposite sides 12a, 12b of the conductive sheet 12 electrically connect to two different voltage levels, resulting in a voltage gradient on the conductive sheet 12. The voltage gradient is perpendicular to y-axis shown in FIG. 1. Two opposite sides 16a, 16b of the elastic conductive film 16 have two different voltage levels, resulting in a voltage gradient on the elastic conductive film 16. The voltage gradient is perpendicular to x-axis shown in FIG. 1. While a user exerts pressure on the elastic conductive film 16 to make the elastic conductive film 16 touch the conductive sheet 12, the different voltage levels on the conductive sheet 12 and on the elastic conductive film 16 will be changed. A touched position of a finger can be detected by voltage level values of four corner of the elastic conductive film 16.
Fingerprint is a pattern that would touch a plurality of positions, therefore, fingerprint identification function cannot be applied to the touch panel 10. In other words, the touch panel 10 can only detect one touched position at a time
Referring to FIG. 2A and FIG. 2B. FIG. 2A is a top view of a typical touch panel 20 with fingerprint identification function. FIG. 2B is a cross-sectional view of touch panel 20 shown in FIG. 2A along cross-sectional line a-a. The touch panel 20 comprises a thin film transistor substrate 21, a plurality of conductive islets 27, an elastic conductive film 28, and a sealant layer 29.
The thin film transistor substrate 21 comprises a base 25, an array of thin film transistors 22, a plurality of data lines 24, a plurality of scan lines 26, and an protective layer 23. The plurality of data lines 24 are vertical arranged on the base 25, the plurality of scan lines 26 are horizontal arranged on the base 25 and across the plurality of data lines 24 to divide into a plurality of sections (no shown). Each of the thin film transistors 22 is respectively located on each of the sections, wherein each drain of the thin film transistors 22 connects adjacent to each data line 24, and each source of the thin film transistors 22 connects adjacent to each data line 24. The protective layer 23 is formed on the base 25 for protecting the array of thin film transistors 22, the plurality of scan lines 26, the plurality of data lines 24.
A plurality of conductive islets 27 are formed on the thin film transistor substrate 21. Each of conductive islets 27 is electrically and respectively connects to each source of the thin film transistors 22 through each of through holes (no shown) formed in protective layer 23. The sealant layer 29 is formed between the plurality of conductive islets 27 and the elastic conductive layer 28 formed above the plurality of conductive islets 27. The sealant layer 29 is formed on the thin film transistor substrate 21, and is located in a periphery area of the thin film transistor substrate 21. In other words, the sealant layer 29 is surrounding the edge of the thin film transistor substrate 21.
While a touch pen, for example, exerts pressure on the touch panel 20 to make a portion of the elastic conductive film 28 touch in corresponding to a portion of the conductive islets 27, at least a signal is generated from the portion of the conductive islets 27, and further is transmitted in corresponding to at least one source of the thin film transistors 22. Furthermore, the thin film transistor substrate 21 can scan signals by the plurality of scan lines 26 so as to detect positions of the signals by the plurality of data lines 24 to determine the touched positions.
Compared the touch panel 10 of FIG. 1 with the touch panel 20 of FIG. 2, the touch panel 20 can detect multi-touched positions at a time; however, the touch panel 10 can only detect a touch position at a time. The thin film transistor substrate 21 scans signals, and further determines the touched positions in a short time. For example, a scan of all signals, from all of the thin film transistors 22, only need 16 milliseconds, at a scanning frequency of 60 Hz. Therefore, the touch panel 20 is able to detect a plurality of touched positions. Utilizing integrated circuit fabrication techniques to fabricate the plurality of thin film transistors 22, the touch panel 20 is capable of detecting extremely small features or patterns, ex. application of fingerprint identification.
However, in the prior arts, the elastic conductive film 28 is only supported by the sealant layer 29 to be located above the conductive islets 27. The sealant layer 29 is formed on a periphery area of the thin film transistor substrate 21, so an interior portion of the elastic conductive film 28 is supported by nothing. The elastic conductive film 28 is generally made of a flexible material, such as polyethylene terephthalate (PET), polymethyl methacrylate (PMMA), polycarbonate (PC), polypropylene (PP), polyethylene (PE), or like as. Therefore, the surface flatness of the elastic conductive film 28 is not easy to be controlled while fabricating the touch panel 20.
After the touch panel 20 is used for a long period, the strength of the elastic conductive film 28 usually drops because of continuous pressings. The flatness of the elastic conductive film 28 is also destruct because of fatigue. While the strength of the elastic conductive film 28 usually drops to a level that the elastic conductive film 28 is not able to be separated from the conductive islets 27, the signals will be constantly generated without exerting any pressure. Then, the touch panel 20 is totally broken.
The touch panel 20 can also be made of transparent material so as to be applied to a surface of a display panel, a monitor, or a tablet computer. Light from the display panel and finally reaching the user's eyes has to be transmitted through the touch panel 20. So the flatness of the elastic conductive film 28 becomes an important condition to displaying quality.
In the prior arts, an initial solution to the above mentioned problems is using ball spacers 14, which are formed on the thin film transistor substrate 21 by spin coating. Then further utilizes a baking process to make ball spacers 14 solidified to support the interior area of the elastic conductive film 28. But there are still two problems: First, the thin film transistor substrate 21 will be contaminated or corroded by the solution of the initial materials of the ball spacers 14. This would lower the detecting sensitivity. Second, because the spin coating method, the ball spacers 14 are generally and disorderly distributed on the thin film transistor substrate 21. Size of the ball spacers is also not of even, so the flatness of the thin film transistor substrate 21 is therefore defeated. An even worse situation is that some positions lose its detecting ability because of the location-disordered and size-unequal ball spacers 14. Therefore, this prior solution cannot effectively solve the above-mentioned problems.
Therefore, improving the remaining drawbacks of the prior arts and further enhancing quality, stability, and product life time of the touch panel is an important issue to the related technique field.